Known obturators have a tapered shaft with a round or oval cross-sectional shape and come in various diameter sizes. After properly cleaning and shaping the root canal, the correct obturator size is determined by using size verifiers with uncoated cores and with different diameters. The diameters of the size verifiers usually correspond to the shaft diameters of coated obturators. A loose fit is essential to provide clearance for allowing surplus gutta-percha material to flow back. A too tight fit may prevent the obturator from reaching the required depth. The obturator is to be inserted with the tip of the obturator reaching the apex of the canal.
The filler body is typically gutta percha, compounds of gutta percha and polymer materials or a similar material with the desirable characteristic to function as a root canal filler. At ambient temperature the filler material is relatively rigid. Before the obturator with the gutta-percha filler is applied to the root canal, the filler material is heated over an open flame or in an oven to an operating temperature at which the filler material becomes semi-molten or plasticized, whereupon the obturator is inserted in the root canal to obtain a three-dimensional filling thereof. The obturator is inserted by using a mild pressure to the working distance and not moved anymore, i.e. the filling is realized with a single insertion. The handle or excess part of the shaft is removed by any suitable technique that applies little or no force to the obturator. This method results in good apical seal and can be performed relatively fast, which is of advantage to both dentist and patient and reduces the risk of wetting or contaminating the root canal.
It is highly desired that the canal is filled as completely as possible. The latter is relatively easy to accomplish if the root canal is regularly shaped and the preparation of the canal has the proper smooth and tapered form. However, the root canal is often irregularly shaped due to resorption during an infection of the channel. Resorption causes the walls of the root canal to dissolve and form fissures and recesses that are difficult to fill. It is therefore possible that the root canal widens again in an area close to the apex. The recesses, fissures and widening apex areas make it very difficult with conventional obturators to obtain a complete fill, since the molten or plasticized gutta percha does not build up a pressure of significant magnitude when it is inserted into the root canal (the gutta percha can flow back out of the root canal at relatively low pressures because there is no provision to block or pressurize the open end of the tooth).
Attempts to solve this problem have been made in the past. U.S. Pat. No. 5,083,923 discloses a method of obturating an extirpated root canal utilizing two types of filler material, one type of which is in the form of a gutta-percha point and the other type of which is a thermoplasticized gutta-percha having a melting temperature of about 15 to 20° C. less than the melting temperature of the gutta-percha point. The steps of the method include the introducing of an initial amount of thermoplasticized gutta percha in a heated and softened condition into the root canal so that the initial amount fills the bottom of the canal. A gutta-percha point is then positioned within the root canal and another amount of thermoplasticized gutta-percha is introduced in a heated and softened condition into the canal. The thermoplasticized gutta-percha is then manipulated into contact with the portion of the gutta-percha point positioned within the root canal so that the gutta-percha point is mixed with the thermoplasticized gutta-percha and worked against the wall until all the gutta-percha is compacted within the root canal. The mixing of the gutta-percha point with the thermoplasticized gutta-percha is performed by applying rotary and reciprocal motions with an instrument like a rotary root canal file. Additional amounts of thermoplasticized gutta-percha are introduced and manipulated into contact with additional gutta-percha points as necessary to fill the complete root canal with a core of filler material. A certain pressure on the semi molten gutta-percha is achieved with this method. However, a disadvantage associated with this method is the fact that the gutta percha filling needs to be machined for some time, and that the process has to be repeated several times in order to fill the complete canal, i.e. it is a time consuming procedure.
Conventional filler material has an operating range between 110 and 130° C. at which it becomes plasticized and is ready for insertion into the prepared root canal.
This relatively high temperature has several disadvantages, such as exposure of the tooth material surrounding the root canal to high temperatures, and the risk of burning due to inadvertent contact of the patient and/or the dental practitioner with the hot obturator or with the oven.